Process of making cellulose acetate



Patented July 7, 1925.

UNITED s'ra'rss PAUL C. SEEL, OF ROCHESTER, NEW YORK,.ASSIGNOR TO EASTMAN KODAK COMPANY,-

01 BOCmTEB, NEW YORK, A CORPORATION OF NEW YORK. PROCESS OI MAKING JELLULOSE ACETATE...

No Drawing.

To all whom it may concern:

Be it known that I, PAUL 0. Sam, a citizen of the United States of America, residing at Rochester, in the county of Monroe and State of New York, have invented certain new and useful Improvements in Processes of Making Cellulose Acetate, of which the following is a full, clear, and exact specification.

This invention relates to processes for making cellulose acetate. One object of the invention is to provide a process in which the fibrous cellulose undergoes such treatment that the acetylatin operation takes place practically uniform y throughout the reaction mass. Another object of the invention is to provide such a process in which fibrous cellulose is first brought to a physical state, in which it does not ball up or otherwise become highly impermeable in spots and is then intermixed with the acetylating bath which difl'uses rapidly through the mass of conditioned fibers and attacks them throughout so as to insure substantial homogeneity in the acetylated product. Other objects will hereinafter appear.

In the manufacture of cellulose acetate it is desirable that the acetylating bath act on all the fibers to practically the same degree. To attain this end, it is important that the fibers and the bath become quickly and uniformly intermixed so that the fibers will become acetylated and dissolved up at substantially the same rate, and thus be under chemical action for approximately the same time throughout the reaction mass. On account of the nature of the bath there is a. tendency for the fibers to ball up or become twisted in rope-like masses which, temporarily at least, become gelatinous toward their outer surfaces and interfere with the penetration of the bath to the interior fibers of the clumps. This sometimes occurs even with carefully shredded fibers, such as are obtained from rag stock, for instance, by mechanical working.

I have found that the fibers can be brought into a condition which promotes rapid and uniform permeation by the acetylating bath and consequent practical homogeneity of the product by bringing the fibers to the form of a pulp and subjecting this pulp to a picker-action in which small aggregates of the wet fibers are torn out. These are dried and form rather flufiy perapplication and June 5, 1924. Serial Ho. 718,174.

meable aggregates twhrich, nevertheless, will mamtaln, at least pa tial identity, and do not clump or ball up into 'difiicultly permeable masses. By maintaining at least partial identity I mean that most of the bers in each aggregate remain together in Since my lnvention is especially useful in connection with the utilization of ra stock in the production of cellulose acetate, shall describe it in connection with such material by way of example. But it will be understood that the invention is not restricted to this illustration, except as indicated by the claims. I can utilize, for instance, any type of rag, new or used, white or colored.

Such rags are immersed in the water in a beater, such as is used, for example, in the manufacture of paper. Of course, any similar type of machine which produces the same mechanical efi'e'ct can be substituted. The fibers of the rags are torn apart and shortened until a good flowable pulp is obtained. If the rag stock is colored, it may be bleached elther prior to beating or during the beating operation, sa by the addition of the usual paper stock leaching reagents to the water. The ulp or flowable stock is then drained and t e excess of water mechanically removed, say by pressing it out between s ueeze rolls. The ulp is then not flowable, at is still slight y moist to the touch. In other words, it is in a self-sustaining condition when made into masses.

The dewatered pulp is then put through a picker, such as is used in the textile indus try say, for example, intreating cotton linters. This includes a multitude of small points which are drawn into contact with the mass of pulp each point picking or tearing off a small aggregate of fibers which maintain, at least artially, their identity in the more or less ufl'y mass which is produced. In other words, each aggregate is coherent.

The picked or pilled, but still moist ma- The dried ag- I III terial, is then thoroughly dried by any suitable means, thereby forming-fluff permeable aggregates which do not readily ballup or rope-up in acetylating baths. In other words, the mass is in a substantially permanent dematted condition which insures uniform penetration of the liquid.

Finally the prepared flufi'y penetrable aggregates are treated with the acetylating bath, either by being stirred into it or by having the latter flowed or rapidly mixed in with them. Any known or preferred fluid acetylating bath may be employed; such, for example, as that disclosed 1n U. S. Reissue Patent No. 12,637, Miles, Apr. 23, 1907, Cellulose derivative and process of making the same.

Where the original fibrous material has the fibers properly separated and shortened, it can be directly mixed up with enough Water to bring it directly to the state in which it is adapted for the picker-action. In other words, if the material is received in a state which is equivalent to that produced by a beater, the process is simplified. Often, however, the fibers are received merely in the form of rag stock and the beating action as described above is necessary.

Having thus described my invention, what I claim as new and desire to secure by Let ters Patent is:

1. The process of making cellulose acetate, which comprises subjecting a moist but selfsustaining pulp of cellulose fibers to a picker-action to form aggregates therefrom, which maintain, at least partially, their dentity, drying the aggregates and treatlng sa1d aggregates with an acetylating liquid.

2 The process of makin cellulose acetate, which comprises beating fibrous cellulose to a flow-able aqueous ulp, removing the bulk of the water until the pulp is moist, but unflowable, subjecting the still moist pulp to picker-action, drying the resulting aggregates and treating said aggregates with an acetylating liquid.

.3 The process of making cellulose acetate, WlllCll comprises beating rag stock in water to se arate the rag fibers, the pulp being flowa 1c, pressing out water until an unfiowable pulp remains which is still moist to the touch, subjecting said still moist pulp to picker-action to pull it into small aggregates, drymg sa1d aggregates to leave them flufli'y but coherent, and treating said aggregates in an acetylating bath.

4 The process of making cellulose acetate, whlch comprises producing a flowable aqueous pulp of bleached, separated, shortened fibers by beatlng rag stock, pressing out water from the pulp until the pulp becomes uuflowable but moist to the touch, picking sa1d still moist pulp into small aggregates, drylng sa1d aggregates to leave them flufl'y, porous, coherent and non-balling, and subect ng sa1d aggregates to an acetylating l1qu1d substantially uniformly dilfused through said aggregates.

Signed at Rochester, New York, this 23rd day of May, 1924.

PAUL C. SEEL. 

